I think I may need a filling. I feel a small crack in between my gum line and front tooth. It is sensitive to hot and cold. I am brushing with a sensitive toothpaste with enamel rebuild. I used to use a mouthwash but it gave me a really painful canker sore. I am scared to go because every time I get work done, I feel this sharp and uncomfortable cold sensation. Do I need a filling? What can I do to not feel that cold sensation?